Lithium ion secondary batteries and electric double-layer capacitors are known as electrical storage devices.
Generally, in comparison to the electric double-layer capacitor, the lithium ion secondary battery has higher energy density and is capable of operation over a longer time interval.
On the other hand, in comparison to the lithium ion secondary battery, the electric double-layer capacitor is capable of rapid electrical charging and discharging, and working life over repeated uses is longer.
Moreover, in recent years, a lithium ion capacitor has been developed as an electrical storage device that combines such respective advantages of the lithium ion secondary battery and the electric double-layer capacitor.
For example, for an electric double-layer capacitor, the applicant of the present application in Patent Document 1 provides “an electrode material for an electric double-layer capacitor using a polyaniline/carbon composite produced by forming a composite of polyaniline or a derivative thereof and a carbonaceous material selected from the group consisting of activated carbon, Ketjen black, acetylene black, and furnace black, where the polyaniline or a derivative thereof is dedoped by base treatment of conductive polyaniline or a derivative thereof dispersed in a nonpolar organic solvent.” The applicant of the present application in Patent Document 2 provides “a polyaniline/porous carbon composite produced by forming a composite of porous carbon material and conductive polyaniline or a derivative thereof dispersed in a doped state in a nonpolar organic solvent.”
Moreover, for a lithium ion capacitor, the applicant of the present application in Patent Document 3 proposes “an electric double-layer capacitor including (i) a positive electrode, (ii) a negative electrode containing such active material as can reversibly absorb and release the lithium ion, and (iii) an electrolyte solution comprising an aprotic organic solvent containing a lithium salt supporting electrolyte. In such an electric double-layer capacitor, the positive electrode contains a collector and electrode active material, using an conductive polyaniline/porous carbon composite produced by forming a composite of an conductive polyaniline or a derivative thereof dispersed in a doped state in a nonpolar organic solvent and porous carbon material as active material, as well as an electric conduction auxiliary agent and a binding agent as may be required.”
On the other hand, Patent Document 4 describes “an electric double-layer capacitor composed of a polarizable electrode immersed in an electrolyte solution, wherein an electrolyte solution is used that includes an electropolymerizable polymer precursor as an additive at 0.005 to 0.05 M concentration; by performing initial charging, the electropolymerizable polymer precursor contained in the electrolyte solution undergoes electropolymerization; the polymer generated by the electropolymerization precipitates at electrochemically active sites present on the positive electrode-side polarizable electrode surface; and the electrochemically active sites are coated by the polymer.”